https://blog-st.tistory.com/entry/Python-OpenCV-%ED%95%9C%EA%B8%80%EC%9C%A0%EB%8B%88%ED%8A%B8%EC%BD%94%EB%93%9C-%EA%B2%BD%EB%A1%9C-%EC%9D%B4%EB%AF%B8%EC%A7%80-%EC%97%B4%EA%B8%B0%EC%A0%80%EC%9E%A5